Computing devices, such as notebook computers, personal data assistants (PDAs), and mobile handsets, have user interface devices, which are also known as human interface devices (“HID”). One type of user interface device that has become more common is a capacitive sense interface. This technology is often referred to as capacitive touch-sense technology; however, this term is a misguided term since the user need not actually physically touch the interface to operate the technology. Rather, the user need only bring a conductive object (e.g., a finger) in close proximity to the capacitive sense interface.
Capacitive sense interfaces may assume a variety of shapes and sizes. FIG. 1A illustrates a conventional circular slider interface 105 having a center mechanical button 110. The illustrated circular slider interface 105 includes eight radial capacitive sensors 115 encircling mechanical button 110 and a processing device 120. Processing device 120 monitors capacitive changes in each of capacitive sensors 115 to register user interactions with circular slider interface 105. Circular sliders may be used to convey absolute positional information of a conductive object, such as to emulate a mouse in controlling cursor positioning on a display, or to emulate a scrolling function of the mouse, but may also be used to actuate one or more functions associated with the sensing elements of the sensing device.
FIG. 1B illustrates a conventional linear slider interface 130. Linear slider interface 130 includes a surface area on which a conductive object may be used to position a cursor in the x-axis (or alternatively in the y-axis). Linear slider interface 130 may include a one-dimensional array of capacitance sensors 135. When making contact or coming in proximity with a particular portion of linear slider interface 100, the individual capacitive sensors 135 will sense capacitive variations that are translated into absolute or relative user interaction position. The capacitance variation may be sent as a signal to a coupled processing device (not illustrated) for analysis. For example, by detecting the capacitance variation of each sensor element, the position of the changing capacitance can be pinpointed. In other words, it can be determined which sensor element has detected the presence of the conductive object, and it can also be determined the motion and/or the position of the conductive object over multiple sensor elements.
FIG. 1C illustrates a conventional touch pad interface 140. Touchpad interface 140 is often used in notebooks to emulate the function of a personal computer (“PC”) mouse. A touch-sensor pad is typically embedded into a PC notebook for built-in portability. Touch pad interface 140 can replicate mouse x/y movement by using two defined axes which contain a collection of sensor elements that detect the position of a conductive object, such as a finger. Mouse right/left button clicks can be replicated by two mechanical buttons, located in the vicinity of the touchpad, or by tapping commands on touch pad interface 140 itself. Touch pad interface 140 provides a user interface device for performing such functions as positioning a cursor, or selecting an item on a display. Touch pad interface 140 may include multi-dimensional sensor arrays for detecting movement in multiple axes. For example, touch pad interface 140 may be implemented as a two-dimensional array of linear sliders.
As consumer electronic devices continue to shrink so to do their user interfaces. A smaller capacitive sense user interface typically means smaller individual capacitive sensors within the user interface. Shrinking the size of a capacitive sensor adversely affects its sensitivity, resulting in a detrimental effect on the user experience. Decreased sensitivity due to shrinking sensor size can be partially compensated by increasing the sampling time of a particular capacitive sensor. However, increasing the sampling time for each capacitive sensor within an array of capacitive sensors reduces the response time of the user interface—once again with detrimental effects on the user experience.
As capacitive sense technology is introduced into other more durable consumer products, such as white goods (e.g., kitchen appliances), the overlay material that protects the capacitive sensors must typically be thicker and more durable to protect the underlying electronics from harsher environments. The thicker dielectric materials also adversely impact the sensitivity of capacitive sense user interfaces.